1. Field of the Invention
The present invention relates to a shift operation control system for outboard motors including a forward/reverse-switching mechanism that switches between a forward position, a neutral position, and a reverse position in response to the operation of a shift operation lever.
2. Description of the Related Art
Conventionally, the outboard motors are equipped with a forward/reverse-switching mechanism disposed between a drive shaft connected (or gear-connected) to the crankshaft of an engine and a propeller shaft as the rotating shaft of a propeller, for switching between the forward position, the neutral position, and the reverse position.
The forward/reverse-switching mechanism is comprised of a drive gear fixed to the lower end of the drive shaft, a forward gear and a reverse gear rotatably disposed on the propeller shaft, which are meshed with the drive gear, and a dog clutch disposed between the forward gear and the reverse gear, for being shifted to one of the neutral position, the forward position, and the reverse position, whereby the shift position is switched between the neutral position, the forward position, and the reverse position.
In this type of forward/reverse-switching mechanism, when a shift operation is carried out from a state in which one of the forward gear and the reverse gear is meshed with the dog clutch, the dog clutch is sometimes difficult to pull off and remains meshed with the gear. To overcome this problem, there has been proposed a system for facilitating the shift operation, in which load applied to the shift operation lever (a force for operating the shift operation lever or a pulling force) during the shift operation is detected, and when the detected load is not lower than a predetermined load (load setting value), the output from the associated engine (engine output) is reduced by turning ignition off (misfiring control) or the like (see e.g. Japanese Laid-Open Patent Publications (Kokai) No. S63-137098, S63-195094, H01-182196, and H02-216391).
Further, when the shift operation is carried out on the onboard motor to switch from the neutral position to the forward position or the reverse position, the dog clutch instantaneously connects between a rotating part of the engine and a gear part of the propeller, which generates a substantial shock (impact) when the gear part of the propeller is in stoppage. Further, immediately after the shift operation, a hull in which the outboard motor is installed receives shocks (vibrations) generated due to the propeller thrust. To eliminate these inconveniences, there has been proposed a method in which when the engine is idling and the shift operation lever is detected to have left the neutral position, the engine speed is controlled to be reduced, and when a shift operation is detected, the control for reducing the engine speed is cancelled (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2001-152897).
However, in the case of a conventional control method used in the system described above, in which the load acting on the shift operation lever during operation thereof is detected, and when the detected load is not lower than the predetermined load, the engine output is reduced, it is difficult to accurately detect the load acting on the shift operation lever due to the influence of the magnitude and stability (torque variation) of drive torque of the engine of the outboard motor, and practically difficult to set the load setting value.
Further, according to this conventional control method, the engine output (drive torque) is not reduced until after the load on the shift operation lever (i.e. the magnitude of a force for operating the shift operation lever) has reached the predetermined value during the shift operation, and therefore the force required for the shift operation becomes larger than the predetermined value before the drive torque is actually reduced, which makes it impossible to easily operate the shift operation lever.
On the other hand, to reduce the shock (shift shock) occurring during the shift operation, it is essential to quickly detect the shift operation. If a switch for detecting the shift operation is configured to detect the shift lever leaving from the neutral position in earlier timing, a shift operation not according to the operator's intention to carry out the shift operation lever is detected, and therefore an erroneous detection tends to occur. Conversely, if the switch is configured to detect the shift lever leaving from the neutral position in later timing, the detection of the shift operation becomes too late to reduce the shift shock sufficiently.
Further, in the conventional method of lowering the engine speed upon detection of the shift operation, a state of operation or position of the shift operation lever after the shift operation is carried out cannot be detected, and therefore, if the shift operation lever is stopped at a position which is neither the neutral position nor the forward or reverse position, the engine speed reduction control continues to be carried out.